High energy fuels



Oct. 9, 1962 R. A. FRANZ ETAL 3,057,704

HIGH ENERGY FUELS Filed June 22, 1959 FIGURE l.

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l5 l7 l9 2| AROMATIC l6 DESULFUR- l8 HYDROGEN- 2Q EXTRACTION IZATION ATION INVENT0R.5

RAYMOND A. FRANZ J SPLANE 3,057,704 HEGH ENERGY FUELS Raymond A. Franz and Leo 5. Spillane, El Dorado, Ark., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Filed June 22, 1959, Ser. No. 821,947 2 Claims. (Cl. 4470) This invention relates to improved high energy fuels and in particular to fuels suitable for use in turbojet and turboprop engines.

One object of this invention is to provide a hydrocarbon fuel having substantially increased energy content per unit volume over hydrocarbon fuels of the prior art.

Another object of this invention is to provide a hydrocarbon fuel for jet engines having a heat of combustion of from 125,000 B.t.u.s to 160,000 B.t.u.s per gallon.

Another object of this invention is to provide a hydrocarbon fuel for jet engines having a heat combustion in excess of 18,000 B.t.u.s per pound.

An additional object of this invention is to provide hydrocarbon fuels for jet engines utilizing hydrocarbon streams obtained in conventional refinery operations.

A particular object of this invention is to provide hydrocarbon fuels for jet engines having exceptionally high energy contents per unit of volume and exceptionally low pour points.

i Additional objects will become apparent from the des'cription of the invention.

Present jet fuels have a heat of combustion of only about 112,000 B.t.u.s per gallon. Higher energy contents per unit volume are desirable. Present jet fuels are also characterized by rather high pour points which severely limit their applicability.

It has now been found that compositions comprising a hydrogenated desulfurized aromatic extract of slurry oil containing a minor amount of tetrawax phenyl benzoate are exceptionally useful high energy fuels characterized by an extremely high energy content per unit of volume and an extremely low pour point. The following examples illustrate the novel compositions of this invention.

Example I A high energy fuel was prepared by mixing 0.1% by weight of total composition of tetrawax phenyl benzoate with the hydrogenated desulfurized aromatic extract of slurry oil. The resultant composition had a pour point of -20 F. The hydrogenated desulfurized aromatic extract of slurry oil utilized in preparing this composition had a pour point of 15 F.

Example 11 A composition was prepared by mixing 0.2% by weight of total composition of tetrawax phenyl benzoate with the hydrogenated desulfurized aromatic extract of slurry oil. The resultant composition had a pour point of -45 F., a heat of combustion of 18,400 B.t.u.s per pound, a heat of combustion of 137,200 B.t.u.s per gallon, an n of 1.4831 and a specific gravity at 20/4 C. of 0.8951. The hydrogenated desulfurized aromatic extract of slurry oil utilized in preparing this composition had a heat of combustion of 18,493 B.t.u.s per pound, a heat of combustion of 136,441 B.t.u.s per gallon, a pour point of l5 F., an n of 1.4837 and a specific gravity of 2'0/4 C. of 0.887.

The novel high energy fuels of this invention comprise the hydrogenated desulfurized aromatic extract of slurry oil and only minor amounts of tetrawax phenyl benzoate. From 0.001 to about 5% by weight of total composition of tetrawax phenyl benzoate has been found to be useful and from 0.05% to about 1% by weight of total composition of tetrawax phenyl benzoate has been found to be ice particularly advantageous. The tetrawax phenyl benzoate can be incorporated into the hydrogenated desulfurized aromatic extract of slurry oil by any convenient manner. No special technique or method is needed.

The tetrawax phenyl benzoates utilized in the practice of this invention are fully described in US. Patents 2,048,465 and 2,138,809.

The hydrogenated desulfurized aromatic extract of slurry oils utilized in preparing the novel compositions of this invention are described and claimed in copending ap plication Serial No. 817,848, filed June 3, 1959.

FIGURE 1 represents a schematic flow diagram of the process utilized for the preparation of the hydrogenated desulfurized aromatic extract of slurry oil.

In the drawing, crude oil is introduced via line 1 into topping column 2. In this column gas is taken overhead 3, straight run gasoline is removed from an upper portion 4 of the column, lube oil stock is removed from the bottom portion 5 of the column, and flux oils are removed as bottoms 6 from the column. A 300-600 C. charge stock is removed via line 7 from an intermediate section of the column and introduced into a catalytic cracker 8. The cracked products from the catalytic cracker are fed via line 9 into column 10 where gas is removed overhead 11, gasoline removed via line 12 from the upper portion of the column, cycle oils, a 200-3 00 C. cut, are removed from the bottom portion of the column via line 13 and slurry oil, boiling above 300 C., is removed as column bottoms via line 14. This slurry oil generally contains about equal portions of paraflins and aromatics.

According to the process of this invention, this slurry oil is then introduced into an aromatic extraction system 15 where the aromatics are removed from the slurry oil by extraction. The overall recovery of parafiin layer from the slurry oil in a furfural extraction amounted to 45.3% of the charge. Recovery of the aromatic oil amounted to 59.2% of the charge. The extraction was carried out in two stages, using two volumes of oil for each volume of furfural. The aromatic-furfural layer was separated and the furfural removed by distillation.

The aromatic extract of the slurry oil is then fed via line 16 to the desulfurization unit 17. In this unit, the aromatic extract is desulfurized. In a particular run the aromatic extract of slurry oil containing 4.72% sulfur was desulfurized with hydrogen over a cobalt molybdenum sulfide catalyst. An average reaction temperature of 395 C. was maintained and an average reaction pressure of 1200 p.s.i.g. was maintained. The sulfur content of the desulfurized material was reduced to 0.07%.

In order that the subsequent hydrogenation reaction can be carried out in a manner conducive to the greatest possible hydrogenation catalyst life, it is advisable that the sulfur content of the aromatic extract of slurry oil be reduced to substantially zero. This at times may require extraordinary desulfurization techniques. For example, .in a particular run it was found that the desulfurized aromatic extract of slurry oil as above described containing 0.07% sulfur could be treated with metallic sodium at 230 C. to effect complete removal of the sulfur still remaining. This significantly increased the catalyst life in the hydrogenation step.

The desulfurized aromatic extract of slurry oil is then fed via line 18 to hydrogenation system 19 wherein the material is completely hydrogenated. In a particular example, the desulfurized aromatic extract of slurry oil was hydrogenated over Raney nickel at a temperature in the range of from about 360 C. to 380 C. and a hydrogen pressure of approximately 2000 p.s.i.g. Substantially complete conversion of the aromatics to naphthenes was column 21 where approximately 90% of the product is taken overhead as high energy fuel and approximately of the product discarded as bottoms.

In a typical operation, a high energy fuel was obtained having a heat of combustion of 18,493 B.t.u.s per pound and 136,441 B.t.u.s per gallon and a pour point of l5 F. The material had a specific gravity at /4 C. of 0.887 and an 11 of 1.4837.

Conventional catalytic hydrocarbon cracking operations, well known to those skilled in the art, can be used to prepare the heavy hydrocarbon oil streams from which the aromatics are extracted, desulfurized and then hydrogenerated to produce high energy hydrocarbon fuels of this invention. Silica and alumina are conventional catalysts which can be employed in the cracking step and these catalysts may be either natural or synthetic. The catalyst can be employed as a fixed bed, as a fluidized solid or as a moving bed, all of which are techniques well known to those skilled in the art. Any of the conventional feeds can be used in the catalytic cracking operation. Such feeds are usually petroleum oils containing a substantial portion boiling above 300 C. Heavy distillates boiling from 300-600 C., or topped or reduced crude oils are typical feed materials. Temperatures in the range of from about 425 C. to about 550 C. are generally employed in the cracking step. Cracking pressures are generally relatively low, varying between atmospheric and 75 p.s.i.g. Most cracking operations generally employed are of the regenerative type wherein the catalyst is periodically regenerated by burning with an oxygen containing gas. The cracking operation can be carried out in a once through system in which there is no recycle and only fresh feed is charged to the unit, or a portion of the eflluent can be separated therefrom by fractional distillation and returned as recycle to the feed stream to the catalytic cracker.

The products of the catalytic cracking zone or reaction are then fractionated into several fractions including a distillate fraction boiling between about 200 C. and 300 C. which is commonly called cycle oil and a bottoms fraction boiling above 300 C. which is generally referred to as slurry oil.

In preparing the high energy hydrocarbon fuels of this invention, the slurry oil is dearomatized to remove therefrom aromatic hydrocarbons. This dearomatization can be carried out by any technique well known in the art but is most conveniently carried out by a solvent extraction. The manner in which this solvent extraction is carried out is not critical. Any of the known solvents suitable for this purpose can be employed to secure the desired aromatic extract. Furfural, liquid sulfur dioxide, mixtures of phenol and water, and the like are all suitable. The treatment is preferably carried out by countercurrent contact in a series of extraction stages. Furfural is particularly suited for this purpose since it can be used at relatively moderate temperatures and at moderate solvent ratios. If desired, the extraction can also be carried out through the use of solid adsorbent materials useful for this purpose.

The equipment and procedure utilized for carrying out the aromatic extraction is not a critical limitation of this invention. A variety of equipment may be employed.

The aromatic extract of slurry oil can be desulfurized by any of the techniques well known to those skilled in the art. Cobalt molybdenum sulfide, tungsten nickel sulfide, nickel sulfide, and so forth, are all suitable catalysts useful in the practice of this process. Desulfurization can be carried out at pressures ranging from 100 p.s.i.g. up to 2000 p.s.i.g. or even higher if desired in particular circumstances. The desulfurization temperature can be varied from room temperature up to 500 C. or higher if desired. Any of the desulfurization equipment well known to those skilled in the art can be employed in this step of the process.

Any of the conventional techniques can be used to hydrogenate the desulfurized aromatic extract of slurry oil in accordance with the process of this invention. Raney nickel, palladium, platinum, etc., are all catalysts useful in this hydrogenation step. Hydrogenation pressures can be varied from 400 to 3000 p.s.i.g. or even higher if desired depending upon the particular catalyst utilized. Hydrogenation temperatures can be varied from room temperature to 500 C. or higher, again depending upon the particular catalyst employed. Any of the conventional hydrogenation equipment With which those in the art are very familiar can 'be used in the practice of this step of the process.

The fuels of the instant invention are eminently suitable for use in jet engines, particularly turbojet and turboprop aircraft engines.

In the operation of turbojet engines, air is withdrawn from the atmosphere into an air compressor, compressed and delivered to the combustion chamber of the engine where it is mixed with these fuels and the mixture ignited. The resulting burning mixture of the fuel and air is diluted with secondary air and expanded through a turbine which drives the air compressor. In these engines, the hot mixture is expanded in the turbine in such a manner that only sufficient energy is extracted from the gases to operate the compressor. The remaining energy is employed to eject the gases in jet form through a jet pipe into the atmosphere and thereby produce thrust.

In using these fuels in turboprop engines, the operation is essentially the same except that the gases are almost completely expanded in the turbine, i.e., they are expanded almost down to the pressure of the surrounding atmosphere, leaving only a relatively small amount of energy to produce thrust when ejected through the jet pipe. Thus, in turboprop engines, the majority of the energy from the hot expanding gases is used to operate the compressor and the propeller and hence the thrust is obtained primarily from the latter.

In many turbojets and turboprop engines, only a single stage turbine is employed. However, more than a single stage may be employed and, if so, guide vanes are intro duced between each pair of turbine wheels. After leaving the last turbine wheel, the gas enters the jet pipe and is discharged therefrom into the atmosphere.

The fuels of the instant invention may be used advantageously in the spark ignition piston-type aircraft engine, diesel engines, and turbine engines generally, but are particularly suitable for use in ramjet, turbojet, and turboprop aircraft engines. However, when the piston-type and diesel engines are employed, the fuel/air ratios are adjusted so as to achieve substantially complete combustion of the air and fuel.

The fuels of the instant invention may be blended with other materials such as gasoline, kerosene, mixtures of gasoline and kerosene, other aviation fuels, and with present hydrocarbon jet fuels to produce an improved fuel over the presently available fuel. More particularly, the fuels described herein may be added to the present aliphatic hydrocarbon jet fuels having a heat of combustion of about 112,000 B.t.u. per gallon to raise the overall heat of combustion thereof. Moreover, the fuels described herein may be used in combination with fuel additives to obtain improved results as regards burning characteristics, etc.

The heat of combustion as given in this specification represents the heat of reaction between gaseous oxygen and liquid hydrocarbon to produce gaseous carbon dioxide and water.

What is claimed is:

1. A high energy fuel consisting essentially of the hydrogenated desulfurized aromatic extract of slurry oil, said slurry oil being the fraction boiling above 300 C. obtained in the catalytic cracking of a heavy petroleum distillate containing from about 0.001 to about 5% by Weight of total composition of tetrawax phenyl benzoate.

2. A high energy fuel consisting essentially of the hydrogenated desulfurized aromatic extract of slurry oil, said slurry oil being the fraction boiling above 300 C. obtained in the catalytic cracking of a heavy petroleum distillate, containing from about 0.05 to about 1% by weight of total composition of tetrawax phenyl benzoate.

References Cited in the file of this patent UNITED STATES PATENTS Reitf et a1 July 21, 1936 Barnum et a1. June 5, 1956 Gluesenkamp et a1 Oct. 9, 1956 Goretta et a1 Nov. 3, 1959 

1. A HIGH ENERGY FUEL CONSISTING ESSENTIALLY OF THE HYDROGENATED DESULFURIZED AROMATIC EXTRACT OF SLURRY OIL, SAID SLURRY OIL BEING THE FRACTION BOILING ABOVE 300* C. OBTAINED IN THE CATALYTIC CRACKING OF A HEAVY PETROLUEM DISTILLATE CONTAINING FROM ABOUT 0.001 TO ABOUT 5% BY WEIGHT OF TOTAL COMPOSITION OF TETRAWAX PHENYL BENZOATE. 